MrC, in that Manage Attachments box, as you say once you "Select Files" from your computer (up to five), you hit "Upload Files" and they shift to the lower part of the box. I generally hit "Insert Inline" which adds the file names into your message as opposed to the start, but that's an option. If you have files shown that you don't want to use hover your mouse over the box in the lower section and a red "X" will appear in the upper right, click that "X", it asks for confirmation of the delete, and when you confirm it is deleted. You will probably also need to go into the text of your message and delete the image link there, too.

There is indeed a "Sticky" at the start of HotRod Talk that explains the options for posting pictures in different ways - http://www.clubhotrod.com/shop-talk/...es-thread.html